Hydraulic steering circuit and steering apparatus

ABSTRACT

A hydraulic steering apparatus comprises a throttle (10) with a bypass line, eliminating the function of the throttle (10) in the direction of the steering cylinder (2). The throttle (10) is disposed between the control valve (3) of the steering apparatus (1) and the cylinder volume of the steering cylinder (2) on the piston rod side. The throttle (10) is used in connection with hydraulic steering apparatus for slow-moving vehicles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a hydraulic steering circuit for slow-movingvehicles and to a hydraulic steering apparatus therefor, which includesa control valve and a metering pump, wherein the control valve includesan interior control piston, controllable by the steering wheel, and anouter control sleeve connected mechanically to the metering pump,wherein both are disposed concentrically relative to each other, andwherein both are rotatable to a limited degree relative to each otheragainst the force of a spring, and wherein the control piston and thecontrol sleeve have grooves cooperating with each other for connectingthe metering pump to connectors of a steering cylinder.

2. Brief Description of the Background of the Invention Including PriorArt

Steering circuits of this kind are sufficiently known. They compriseessentially a tank, a supply pump, a hydraulic steering apparatus, and ahydraulic steering cylinder. The steering apparatus has, on the onehand, a feed connector and a discharge connector, which are bothconnected to the tank, and, on the other hand, two cylinder connectors,which are in connection with the two cylinder volumes of the steeringcylinder. The steering cylinder, in general, is furnished with aone-sided piston rod, wherein the piston rod transfers its motionmechanically through a steering linkage to the guiding wheels.

Based on the one-sided piston rod, the two cylinder volumes havenaturally different volumes. Upon actuation of the steering apparatus inone rotation direction, metered oil is transported through the steeringapparatus in one of the two cylinder volumes and at the same time theoil is displaced from the other cylinder volume and fed thereby again tothe tank through the steering apparatus. For this purpose, the samegrooves in the control piston are available in the steering apparatusfor the two directions of rotation.

The function of such a steering circuit with a corresponding steeringapparatus is always satisfactory in cases where, corresponding to thecircumstances, a sufficient steering load has to be overcome.

However, in certain individual application cases and applicationlocations, pulling forces can occur at the piston of the steeringcylinder, as is the case, for example, upon fast travel and a highrotation speed of the steered wheel of articulated frame steeredvehicles. This pulling load at the cylinder piston can lead to theelimination of the steering load, based on the small oil volume, on thepiston rod side when steering against the floor of the cylinder piston.Thereby, the steering cylinder runs in advance of the steering motion.An uncontrolled steering behavior is the consequence and is associatedwith all its danger.

A circuit with such a steering apparatus is described in the PrintedPatent document WO-A-9112985, wherein a one-way restrictor is furnishedin the working line between the control valve and the working area ofthe steering cylinder on the piston rod side for decreasing theinfluence of a negative damping relative to the dynamics of vehiclemovement. The check valve is thereby blocked in the direction from thesteering cylinder to the control valve.

This circuit increases the equipment-technological expendituressubstantially.

A corresponding steering apparatus is presented in the printed patentdocument DE-A-2810902, wherein longitudinal control grooves arefurnished in the control piston subdivided in two parts relative totheir length for the purpose of decreasing the interior leak flows.

This solution does not eliminate the uncontrolled behavior of thesteering cylinder in case of a pulling load.

SUMMARY OF THE INVENTION

1. Purposes of the Invention

It is an object of the present invention to create a hydraulic steeringcircuit and a corresponding steering apparatus which assures asufficient steering load in the two steering directions in case of asteering cylinder with a one-sided and pullingly loaded ortension-loaded piston rod.

These and other objects and advantages of the present invention willbecome evident from the description which follows.

2. Brief Description of the Invention

The present invention provides for a hydraulic steering circuit andsteering apparatus, wherein a throttle is disposed in the line betweenthe control valve of the steering apparatus and the cylinder volume ofthe steering cylinder on the piston rod side. The throttle includes abypass line which eliminates the function of the throttle in thedirection of the steering cylinder.

The hydraulic steering apparatus comprises a control valve and ametering pump. The control valve is furnished with an interior controlpiston, controllable by a steering wheel, and an outer control sleevemechanically connected to the metering pump. The control piston and thecontrol sleeve are disposed concentrically relative to each other andare rotatable relative to each other to a limited degree against a forceof a spring and are furnished with feed grooves and discharge groovescooperating with each other. The feed grooves, connected to the meteringpump, and the discharge grooves of the control piston, connected to asteering cylinder, are furnished as axial grooves which are uniformlydistributed over their circumference. The discharge grooves of thecontrol piston are formed with openings toward the interior of thecontrol valve. The discharge grooves furnished in the control piston areformed as a first discharge groove and a second discharge groove. Thefirst discharge groove and the second discharge groove are alignedaxially relative to each other. The first discharge groove iscoordinated to a cylinder volume on a piston side. The second dischargegroove is coordinated to a cylinder volume of the steering cylinder on apiston rod side. The opening of the discharge groove, disposed on thepiston rod side, is furnished as a throttle.

Each of the discharge grooves can be delimited in two axial directionsand the opening of the discharge groove and/or the throttle of thedischarge groove can be furnished as radial boreholes relative to arotation axis of the control piston.

The novel features which are considered as characteristic for theinvention are set forth in the appended claims. The invention itself,however, both as to its construction and its method of operation,together with additional objects and advantages thereof, will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, in which are shown several of the variouspossible embodiments of the present invention:

FIG. 1 is a view of a schematic diagram of a circuit with a firstvariation of a solution;

FIG. 2 is a view of a schematic diagram of a circuit with a secondvariation of a solution;

FIG. 3 is a view of a schematic diagram of a control valve of a steeringapparatus.

DESCRIPTION OF INVENTION AND PREFERRED EMBODIMENT

As the FIGS. 1 and 2 show, the steering circuit includes essentially asteering apparatus 1 and a steering cylinder 2. The steering apparatus 1is composed of a control valve 3 and a metering pump 4 and includes, onthe one hand, a feed connector 5 and a discharge connector 6 and, on theother hand, a cylinder connector 7 for the, for example, left rotation,and a cylinder connector 8 for the then remaining right rotation. Thecylinder connector 7 is connected to the piston rod side and thecylinder connector 8 is connected to the piston side of the steeringcylinder 2. According to FIG. 1, a one-way restrictor 9 is disposedaccording to the invention in the line between the control valve 3 ofthe steering apparatus 1 and the piston rod side of the steeringcylinder 2 in such a way that the one-way restrictor 9 opens in thedirection toward the steering cylinder 2.

A throttle 10 is disposed in the control valve 3 of the steeringapparatus 1 in a groove constructed only for the return flow instead ofthe one-way restrictor 9.

For this purpose, the control valve 3 of the steering apparatus 1 isconstructed according to FIG. 3. The control valve 3, operatingaccording to the rotary slide principle, includes an internal controlpiston 17, controllable by the steering wheel, and an external controlsleeve 11, mechanically connected to the metering pump 4. The controlpiston 17 and the control sleeve 11 are rotatable relative to each otherto a limited degree against the force of a spring 18.

The control sleeve 11 is furnished with a row of boreholes 12 uniformlydistributed at the circumference, and a second row of boreholes 13,uniformly distributed at the circumference, however, directed radiallystaggered in tangential direction with respect to the boreholes 12. Therow of the boreholes 12 and the row of the boreholes 13 can be providedas single rows or multiple rows. The control piston 17 exhibits at itssurface several axial feed grooves 14, distributed uniformly at thecircumference. Axial discharge grooves 15 and 15' are disposed in thecontrol piston 17 also uniformly and with the same subdivision, butstaggered by a half subdivision. All discharge grooves 15 and 15' are ineach case axially delimited toward two sides. Thereby each dischargegroove 15 is also separated from the associated discharge groove 15'.The discharge grooves 15 are in each case connected by an opening 16,and the discharge grooves 15' by the throttle 10, to the interior of thecontrol valve 3 and thus to the discharge connector 6 of the steeringapparatus 1. The cross-section of the opening 16 is selected to berelatively large and is matched to the cylinder volume of the steeringcylinder 2 on the piston side. The cross-section of the throttle isprovided relatively small and is directed toward the cylinder volume ofthe steering cylinder 2 on the piston rod side.

The mode of operation of the hydraulic steering apparatus for mobileplants is generally known.

The oil furnished by a pump is returned again without effect to the tankin a neutral position and based on a corresponding constructive layoutof the steering apparatus 1.

Upon actuation of the steering wheel in one direction, the controlpiston 17 and the control sleeve 11 are rotated relative to each other,and thus the feed connections are released by the metering pump 4 to oneside of the steering cylinder 2. At the same time, the dischargeconnections in the control valve 3 of the steering apparatus 1 open up.

The oil present at the feed connector 5 flows thereby through thecontrol valve 3 and the metering pump 4 and exits at the cylinderconnector 7 from the steering apparatus 1. According to FIG. 1, thecheck valve of the non-return valve with restriction or one-wayrestrictor 9 opens and releases a throttle-free cross-section. Based onthe adjusting pressure on the piston rod side, the piston rod of thesteering cylinder 2 shifts and actuates the wheels to be steered. Theoil is displaced thereby from the cylinder volume on the piston side andpasses in a conventional fashion through the metering pump 4 and thecontrol valve 3 to the tank. In case of a change in the direction ofrotation at the steering wheel, the flow direction of the oil reverses.Now, the oil present in the cylinder volume of the steering cylinder 2on the piston rod side is displaced and passes the one-way restrictor 9only through the throttle opening. In case a normal steering behavior,for example, on a road section with no slope, only small pressure lossesoccur at the one-way restrictor 9, and thus only a negligible steeringload occurs. In the case that a pulling load occurs at the piston rod ofthe steering cylinder 2, for example, on a road section with downhillslope and with a high steering speed at the guided wheel of anarticulated frame steered vehicle, then the pressure loss increases atthe one-way restrictor 9. The banked pressure in front of the one-wayrestrictor 9 opposes the direction of motion of the piston rod with aforce, corresponding approximately to the pulling load. The steeringbehavior remains normal.

In the constructive embodiment of the steering apparatus 1 according toFIGS. 2 and 3, an identical functional behavior is obtained in case of achanged course of the flow of oil. A separate line with differentcross-sections is associated to each cylinder volume of the steeringcylinder 2 in the return line inside of the control valve 3. In case ofthe displacement of the flow of oil from the cylinder volume on thepiston side, the oil passes through the metering pump 4 to the boreholes12 of the control sleeve 11 and from there through the discharge grooves15 and the radial opening 16 to the tank.

In case of the displacement of the oil flow from the cylinder volume ofthe steering cylinder 2 of the piston rod side, the path of the oilagain runs through the metering pump 4 to the boreholes 13 of thecontrol sleeve 11 and from there through the discharge grooves 15' andthe throttle 10 to the tank.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofsteering apparatuses differing from the types described above.

While the invention has been illustrated and described as embodied inthe context of a hydraulic steering circuit and steering apparatus, itis not intended to be limited to the details shown, since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. Hydraulic steering apparatuscomprising a control valve and a metering pump, wherein the controlvalve includes an interior control piston, controllable by the steeringwheel, and an outer control sleeve, mechanically connected to themetering pump, wherein the control piston and the control sleeve aredisposed concentrically relative to each other and are rotatablerelative to each other to a limited degree against the force of a springand are furnished with feed and discharge grooves cooperating with eachother, wherein the feed grooves and the discharge grooves of the controlpiston are furnished as axial grooves with openings toward the interiorof the control valve, wherein the axial grooves are distributeduniformly at the circumference, characterized in that the dischargegrooves (15, 15') are furnished in the control piston (17) subdivided intwo parts in axial direction, that the discharge groove (15) iscoordinated to the cylinder volume on the piston side and that thedischarge groove (15') is coordinated to the cylinder volume of thesteering cylinder (2) on the piston rod side, and that the opening ofthe discharge groove (15') is furnished as a throttle (10).
 2. Hydraulicsteering apparatus according to claim 1, characterized in that each ofthe discharge grooves (15, 15') is limited in the two axial directionsand that the opening (16) of the discharge groove (15) and the throttle(10) of the discharge groove (15') are furnished as radial boreholes. 3.Hydraulic steering apparatus comprising a control valve and a meteringpump, wherein the control valve is furnished with an interior controlpiston, controllable by a steering wheel, and an outer control sleevemechanically connected to the metering pump, wherein the control pistonand the control sleeve are disposed concentrically relative to eachother and are rotatable relative to each other to a limited degreeagainst a force of a spring and are furnished with feed grooves anddischarge grooves cooperating with each other, wherein the feed grooves,connected to the metering pump, and the discharge grooves of the controlpiston, connected to a steering cylinder, are furnished as axial grooveswhich are uniformly distributed over their circumference, and whereinthe discharge grooves of the control piston are formed with openingstoward the interior of the control valve, wherein the discharge groovesfurnished in the control piston (17) are formed as a first dischargegroove (15) and a second discharge groove (15'), wherein the firstdischarge groove (15 and the second discharge groove (15') are alignedaxially relative to each other, and wherein the first discharge groove(15) is coordinated to a cylinder volume on a piston side, and whereinthe second discharge groove (15') is coordinated to a cylinder volume ofthe steering cylinder (2) on a piston rod side, and wherein the openingof the discharge groove (15'), disposed on the piston rod side, isfurnished as a throttle (10).
 4. The hydraulic steering apparatusaccording to claim 3, wherein each of the discharge grooves (15, 15') isdelimited in two axial directions and that the opening (16) of thedischarge groove (15) and the throttle (10) of the discharge groove(15') are furnished as radial boreholes relative to a rotation axis ofthe control piston (17).